1. Field of the Invention
The present invention relates to ribbon cartridges for use in impact type printers such as line printers, typewriters and wire-dot printers and more particularly to an ink transfer roller used in ribbon cartridges for re-inking endless ink ribbons.
2. Prior Art
An impact type printer, such as a wire-dot printer, typically uses a ribbon cartridge that stores therein an ink ribbon which is impregnated with ink. The ink is impregnated in the ribbon by an ink transfer roller. The ink will be depleted long before the ribbon wears out, and as the ribbon's supply of ink becomes depleted, print quality becomes increasingly lighter.
A variety of devices have been proposed to re-ink the ribbon so as to derive further use from the ribbon cartridge. FIG. 1 shows a typical prior art re-inking system. The re-inking assembly is installed in the housing of a ribbon cartridge 10 and includes a re-inking roller 12 which is formed from a porous material saturated with ink and an ink transfer roller 14 which is mounted for rotation tangentially to the re-inking roller 12.
The ink ribbon drive assembly drives and advances an endless loop ribbon 16 so that the ribbon 16 is brought into contact with a portion of the transfer roller 12 as it is advanced along its path. More specifically, ink is transferred from the re-inking roller 12 to the transfer roller 14 and then to the ribbon 16 in a manner that the ribbon is continuously re-inked.
In a typical prior art ink ribbon cartridge as described above, the ink transfer roller 14 is a simple cylinder shape as shown in FIG. 2. In other words, it has a smooth external circumferential surface. With this type of ink transfer roller, the ink is transferred onto the ribbon uniformly along a vertical cross-section of the ribbon because of the smooth and not-contoured surface of the roller. This, however, causes the ribbon concentration to become too high in some places while not being enough in other places, causing inconsistent print quality and less character yield.
In the mean time, some printers and typewriters feed ribbons in an inclined manner so that the print head can make a largest possible contact with the ink ribbon surface. This type of ribbon feeding is shown in FIG. 3. In this type of ribbon feeding, the ribbon 16 is divided into three different regions: the central region 16a, the intermediate regions 16b located on both (upper and lower) sides of the central region 16a, and edge regions 16c located between the intermediate regions 16b and the edges 50d of the ribbon 16. The intermediate regions 16b are printed on one time during each passage in front of the printing head of a printer, and the central region 16a is printed on twice during each passage in front of the printing head. The edge regions 16c are not printed on or not used in printing. Parallel dot lines indicate the paths of the upper and lower end print hammers of the print head (not shown).
In other words, the ink in the central region 16a is consumed twice as much as the ink in the intermediate regions 16b. However, merely with the cylindrical ink transfer roller 14, as shown in FIG. 2, is the ink transferred to the ribbon 16 uniformly. As a result, ink is in fact not applied onto the ribbon 16 from where it was consumed and in the amount that it was used. In addition, the configurations of the characters and symbols to be printed or typed differ greatly, and therefore, ink on the ribbon is not depleted or consumed evenly. Nonetheless, the ribbon is re-inked evenly and uniformly with the prior art cylindrical roller as shown in FIG. 2, and the results are inconsistent print quality and less characteristic yield.